This invention relates to dock loading equipment and in particular to a dock leveler assembly having a barrier which automatically protrudes to prevent vehicles from accidentally running off the front end of the leveler.
Dock leveler assemblies are known and widely used to accomplish the loading and unloading of vehicles which are parked at a loading dock platform. The art is replete with many examples of such dock leveler systems. Generally, they comprise a deck assembly which is mounted in the dock to compensate for variations in height between the fixed loading dock platform and the bed of the vehicle to be loaded and unloaded. Such dock levelers are equipped with a pivotally mounted plate or lip on the front end which serves as a bridge between the leveler and the bed of the vehicle. In use, forklift trucks or the like traverse between the dock and the vehicle across the deck of the leveler and the lip for purposes of moving materials from the vehicle on/off the dock. A safety problem which frequently occurs is that such forklift trucks and the like may run off the exposed end of the dock when no vehicle is parked adjacent thereto.
Within the prior art various techniques have been proposed to provide a physical barrier for the prevention of such run-off of the end of the dock surface. For example, levelers used by the U.S. Post Office employ a lip which extends to the rearward behind the lip hinge so that when the lip falls the rear portion is raised to form a barrier. By this technique, the lip is pivotally fixed to the front edge of the dock having a pivot access of the lip set back from the rear edge thereof. Thus, the rear section of the extending lip between the pivot axis and the lip rear edge projects above the dock ramp surface and forms a barrier. A problem occurring in this system is that a pinch-point hazard exists if the operators foot is near the front of the leveler when the lip is extended.
Another solution is set forth in U.S. Pat. No. 4,920,598, which employs a lip having a series of slots which, when the lip is in its stored depending position and stored by lip keepers provides a projection above the dock leveler surface. When the leveler is moved from its inoperative, stored, position the lip plate slides on the slots downward thus automatically retracting the protruding lip portion forming the barrier and allowing the lip to be raised by hydraulic techniques or the like for normal use.
The solution proposed in the '598 patent has several weaknesses associated with the configuration. First, because it employs a slotted mounting for the lip structure is inherently weakened. Moreover, the sliding components will tend to bind due to wear, corrosion, adverse weather and the like. Secondly, the barrier protrudes between the hinges about which the lip extends. Consequently, the hinge structure itself is weakened because of removal of portions of the hinge tubes thereby eliminating a significant amount of the shear resistance of the hinge pin.
The system also adds a degree of unnecessary complexity to the dock leveler structure by requiring a movable stop to permit the barrier to be lowered.
An alternative embodiment which uses pop-up portions hydraulically actuated defines, at best, an intermittent barrier still suffering from many of the same deficiencies such as weakness of the hinge pin.
Importantly, both the '598 and the prior art "Post Office" configuration are actuated only at dock level. A hazardous condition exists in end-loading below dock level where the leveler slopes downward and any material handling equipment on the leveler is more likely to roll. That is, the leveler is canted downward such that by gravity objects and the like will tend to roll off the end of the dock. End loading is a necessary function of the use of the dock leveler to permit unloading of a vehicle where the cargo is too close to the rear of the truck such that the lip cannot extend. Generally, unloading of a vehicle in that condition can be done with the leveler in the stored cross-traffic position where it is flush with the dock surface. However, if the truck bed is lower than the leveler the lip must be extended slightly beyond the lip keepers and the leveler is then lowered to a below dock position to permit such unloading to take place. In this position the leveler slopes downward away from the loading dock. Neither the '598 patent nor the Post Office design would have a barrier in place in that condition which is the most dangerous since vehicles can run off the end of the dock by rolling movement down the slope. Moreover, in the case of the '598 configuration any truck bed lower than the top of the barrier would require such below dock end loading.